Interfacial Dynamic Length Scales in the Glass Transition of a Model
Freestanding Polymer Film and Their Connection to Cooperative Motion

RJ Lang and DS Simmons, MACROMOLECULES, 46, 9818-9825 (2013).

DOI: 10.1021/ma401525q

Nanoscale confinement alters the dynamics of glass-forming liquids in
films of order 100 nm in thickness. A common hypothesis for the origin
of this long range posits that interfacial dynamics propagate into the
film via cooperatively rearranging regions (CRRs). However, the precise
nature of the dynamic interface remains uncertain, and its
identification with CRRs has yet to be firmly established. Based on
results from coarse-grained molecular dynamics simulations of a
freestanding polymer film, here we show that an apparent qualitative
discrepancy between computational and several experimental measures of
the interfacial dynamic length scale results from a difference in
definition and not from a difference in underlying behavior of
experimental and simulated systems. We then show that the computational
definition exhibits a direct correspondence with the expected behavior
of CRRs as predicted by the Adam-Gibbs theory, and we suggest that it
should be possible to extract this length scale from experimental
measurements.